[Qemu-devel] Re: [Bochs-developers] BIOS, ACPI, CMOS and Windows EvenID: 4

[Sebastian Herbszt]

Gleb Natapov wrote:
> > The Microsoft document suggests to copy the CMOS data to somewhere in memory
> > and access it there. I guess rombios space from 0xe000 to 0xffff could be a good
> > candidate.
> No need to copy the whole CMOS. Copying only memory size should be
> enough. Also putting it somewhere in first 4K should be better. You
> can't write into 0xe000-0xffff unless chipset shadows it in a memory.

bios_shadow_init() from rombios32.c does already support this for the 440fx.

> > The 440fx specs says "The top of memory is determined by the value written into 
> > DRB7."
> > We might get the proper value from there. But it also says "Note that the PMC 
> > supports
> > a maximum of 1 Gbytes of DRAM."
> Yeah, I saw that my real HW takes top of the memory somewhere from the
> chipset and looked in 440fx specs if it has this info, but it turned
> out that we abuse 440fx and sometimes use much more memory that it
> supports. We can re-use DRB registers for our needs and store memory
> size there on POST (we can store 8 bytes there, so it should be enough)
> and read them from AML. Are all users of bochs BIOS uses the same
> chipset?

I think bochs, qemu, xen and virtual box emulate the 440fx.

- Sebastian